This invention relates to ink jet printers, and, more particularly, to a printer wherein the colorant reservoir on the print head may be refilled during normal operation.
Printers are devices that print characters onto a printing medium such as a sheet of paper or a polyester film. Printers of many types are available, and are commonly controlled by a computer that supplies the images, in the form of text or figures, that are to be printed.
Some printers use a colorant-containing liquid, which may be an ink or a dye, but is often termed an "ink" or "liquid toner" in the printer industry, to form the images on the printing medium. (By contrast, other printers use a dry toner to form the image.) Such printers deliver the colorant to the medium using a print head that creates the proper patterning of colorant to permanently record the image.
One type of printer is the ink jet printer, which forms small droplets of colorant that are ejected toward the printing medium in a pattern of dots that form the images. When viewed at a distance, the collection of dots form the image in much the same manner that photographic images are formed in newspapers. Ink jet printers are fast, produce high quality printing, and are quiet, because there is no mechanical impact during formation of the image, other than the droplets of colorant striking the printing medium.
Typically, an ink jet printer has a large number of individual colorant-ejection nozzles in the print head, supported in a carriage and oriented in a facing, but spaced-apart, relationship to the printing medium. The carriage and supported print head traverse over the surface of the medium, with the nozzles ejecting droplets of colorant at appropriate times under command of the computer or other controller, to produce a swath of droplets. In the thermal ink jet printer, the ejection of droplets is accomplished by heating a volume of the colorant adjacent the nozzle with a resistor, thereby vaporizing a bubble of the colorant to drive the droplet toward the printing medium. The droplets strike the medium and then dry to form "dots" that, when viewed together, form one swath or row of the permanently printed image. The carriage is moved an increment in the direction lateral to the traverse (or, alternatively, the printing medium is advanced), and the carriage again traverses the page with the print head operating to deposit another swath. In this manner, the entire pattern of dots that form the image is progressively deposited by the print head during a number of traverses of the page. To achieve the maximum output rate, the printing is preferably bidirectional, with the print head ejecting colorant during traverses from left-to-right and right-to-left.
The colorant is stored in a reservoir that, for some types of printers, is mounted on the carriage adjacent the nozzles. Colorant is then delivered by capillary action to the nozzles for ejection. It is common for some printers that the print head is a single consumable and disposable unit, that may be readily inserted and removed from the printer when the colorant in the reservoir is exhausted or one or more of the nozzles malfunction.
In the early stages of the development of thermal ink jet printers, the useful life of the print head was usually established by the time until a nozzle failure occured. In some cases the colorant ejector system would become inoperable prior to depletion of the colorant in the reservoir. More recently, the design and manufacturing of the nozzles and associated apparatus of the print head have advanced, so that the life of the nozzles prior to failure is lengthened significantly. Thus, the reservoir's supply of colorant may be exhausted before nozzle failures are experienced. There now exists a need for a larger supply of colorant available for ejection.
The design of the reservoir container of the print head is sophisticated, because it is initially filled with colorant and transported to the customer, and thereafter must deliver a flow of filtered colorant without leakage under a variety of conditions such as different orientations of the print head and use of the printer at different altitudes and temperatures. In one present approach, the interior of the reservoir container contains a compliant open cell foam. Colorant is filled into the foam during manufacture. The colorant is retained within the pores of the foam, and slowly flows to the ejector over the life of the print head. Filling of the reservoir container requires great care to avoid pockets of colorant that can leak, air pockets, and defects in the foam that cause irregular colorant flow.
Simply increasing the size of the reservoir container is not an acceptable solution to the problem of providing a larger colorant supply, because the container is supported upon the printer carriage and moves with the nozzle mechanism. Increasing the size of the reservoir container would necessarily increase the size, strength, and cost of the structure that supports and moves the carriage. The performance of the printer would suffer, because of the greater mass of the carriage and container.
There is a need for an approach for increasing the amount of colorant available for droplet ejection in such a print head. The approach should permit the desirable features of the present approach to providing colorant to be retained, provide more colorant, and not unduly increase the cost or complexity of the printer. The present invention fulfills this need, and further provides related advantages.